1. Field of the Invention
The present invention relates to an electrically-driven steering shaft lock device which is applied to a vehicle such as an automobile.
2. Description of the Related Art
Vehicles such as automobiles and the like are equipped with, for example, a so-called electrically-driven steering lock device as an antitheft device. The electrically-driven steering lock device has, for example, a lock body which is assembled to the steering post of the vehicle. A lock bar, which is urged toward the steering shaft by a spring, is provided within the lock body. By making the lock bar protrude out toward the steering shaft and engage with an engagement groove formed in the steering shaft, the steering shaft is locked.
A screw mechanism or a cam mechanism or a reciprocatingly-movable driving body is driven by an electrically-driven motor which is the means for driving the lock bar, and the lock bar, which is engaged with the steering shaft, is pulled out such that the locking is released. See, for example, Japanese Patent Application (JP-A) No. 10-138872.
There are cases in which, in the state in which the lock bar is engaged with the engagement groove of the steering shaft, force in a rotating direction is applied to the steering shaft by the repulsion from the wheel, and lock bar catches on the engagement groove of the steering shaft, and resistance to pulling-out of the lock bar arises. Accordingly, the means for driving the lock bar must have driving force which is sufficient to pull the lock bar out against such resistance.
Here, when a screw mechanism is used as the driving means, a large driving force is obtained, and the device itself can be made compact. On the other hand, there are problems in that, not only does the cost increase, but also, the operation time for pulling out the lock bar is long.
When a cam mechanism is used as the driving means, the cost is lower as compared with a screw mechanism, but the efficiency of converting from rotational motion to rectilinear motion is poor, and the driving force is weak. Therefore, either the motor must be made larger and the output increased, or the gear reduction ratio must be increased, or the like. Therefore, problems arise in that the electrically-driving steering lock device itself becomes large and the cost thereof increases.